Pd embedded in porous carbon (Pd@CMK-3) as an active catalyst for Suzuki reactions: accelerating mass transfer to enhance the reaction rate

Heterogeneous catalysts are promising candidates for use in organic reactions due to their advantages in separation, recovery, and environment compatibility. In this work, an active porous catalyst denoted as Pd embedded in porous carbon (Pd@CMK-3) has been prepared by a strategy involving immersion, ammoniahydrolysis, and heating procedures. Detailed characterization of the catalyst revealed that Pd(0) and Pd(II) species co-exist and were embedded in the matrix of the porous carbon (CMK-3). The as-prepared catalyst has shown high activity toward Suzuki reactions. Importantly, if the reaction mixture was homogenized by two minutes of ultrasonication rather than magnetic stirring before heating, the resistance to mass transfer in the pore channels was significantly reduced. As a result, the reactions proceeded more rapidly and a four-fold increase in the turnover frequency (TOF) could be obtained. When the ultrasonication was employed throughout the entire reaction process, the conversion could also exceed 90% even without the protection of inert gas, and although the reaction temperature was lowered to 30 °C. This work provides a method for fabricating highly active porous carbon encapsulated Pd catalysts for Suzuki reactions and proves that the problem of mass transfer in porous catalysts can be conveniently resolved by ultrasonication without any chemical modification being necessary.[Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

Fabrication and visible-light photocatalytic behavior of perovskite praseodymium ferrite porous nanotubes

Perovskite praseodymium ferrite (PrFeO3) porous nanotubes are prepared by electrospinning of the precursor solution into nanofibers, subsequently by annealing the precursor fibers at a low temperature (e.g. 40 °C) and finally by calcination at a high temperature. The low temperature annealing treatment is found to play a key role in the formation of porous nanotube. The porous tubes show a perovskite-type PrFeO3 crystal characteristic with high optical absorption in the UV-visible region and an energy band gap of 1.97 eV. When compared with PrFeO3 porous nanofibers and PrFeO3 particles, the PrFeO3 porous nanotubes show better visible-light photo-catalytic ability to degrade Rhodamine B in aqueous phase because of the increased surface area and more active catalytic sites on the inner walls and outer surfaces.

Multifunctional polymer/porous boron nitride nanosheet membranes for superior trapping emulsified oils and organic molecules

Effective oil/water separation and removal of organic molecules from water are of worldwide importance for water source protection. Multifunctional sorbent materials with excellent sorption capacity, stability, and recyclability properties need to be developed. Here, flexible and multifunctional polymer/porous boron nitride nanosheets (BNNSs) membranes with high water permeability, exhibiting high effectiveness and stability in the purification of simulated wastewater tainted with either oil/water emulsion or organic molecules, are reported. Remarkably, the flexible nature of these porous membranes enables simplicity of operation for water remediation processing and ease of post-processing collection. The composite membrane also displays a remarkably high permeability of 8 × 10⁴ L μm m^-2 h^-1 bar^-1, roughly three orders of magnitude higher than pure polymer, and excellent filter efficiencies for the pharmaceuticals ciprofloxacin, chlortetracycline, and carbamazepine (up to 14.2 L g^-1 of BNNSs in the composite membrane for a concentration of 10 mg L^-1 ciprofloxacin) and the dye methylene blue (up to 9.3 L g^-1 of BNNSs in the composite membrane at a concentration of 30 mg L^-1). Exhausted membranes can be readily rejuvenated by simple washing with retention of their high-performance characteristics. The results demonstrate the potential efficacy and practicality of these membranes for water cleaning.

The high renaissance properties of porous three dimensional graphene using one step reduction and its application in flexible conductor

 A super conductive graphene with continuous three dimensional (3D) porous structures that can potentially be used as flexible conductors has been produced by one step reduction of graphene oxide (GO) film. The high renaissance properties have been demonstrated by mechanical and electrical results where a noticeable increase in the electrical conductivity to 3850 S/cm has been demonstrated after embedding the 3D graphene foam into nearly insulated polydimethylsiloxane (PDMS). The graphene integrated PDMS film has a higher strain up to 100% elongation compared with the strain of only 60% for PDMS. Fourier transform infrared (FTIR) and x-ray photoemission spectroscopy (XPS) results reveal that most oxidized groups have been removed, which contributes to the renaissance of most outstanding properties of graphene because of the recovery of sp2 carbon structures.

Development of hierarchical porous NiO-YSZ with improved mechanical properties

 The thesis developed an hierarchical porous NiO/YSZ with high mechanical performance using a novel process. This process fabricates initial scaffolds with a controllable porosity by enhancing the surface energy of poly methyl methacrylate (PMMA) for the assembly of NiO-YSZ/PMMA. It maintains the hierarchical porous structure using two-step sintering (TSS) to restrict the growth of nanoparticles, and improves the mechanical properties in combination with a bimodal distribution of NiO/YSZ nano-particles.

Control of partial coalescence of self-assembled metal nano-particles across lyotropic liquid crystals templates towards long range meso-porous metal frameworks design

The formation of purely metallic meso-porous metal thin films by partial interface coalescence of self-assembled metal nano-particles across aqueous solutions of Pluronics triblock lyotropic liquid crystals is demonstrated for the first time. Small angle X-ray scattering was used to study the influence of the thin film composition and processing conditions on the ordered structures. The structural characteristics of the meso-structures formed demonstrated to primarily rely on the lyotropic liquid crystal properties while the nature of the metal nano-particles used as well as the their diameters were found to affect the ordered structure formation. The impact of the annealing temperature on the nano-particle coalescence and efficiency at removing the templating lyotropic liquid crystals was also analysed. It is demonstrated that the lyotropic liquid crystal is rendered slightly less thermally stable, upon mixing with metal nano-particles and that low annealing temperatures are sufficient to form purely metallic frameworks with average pore size distributions smaller than 500 nm and porosity around 45% with potential application in sensing, catalysis, nanoscale heat exchange, and molecular separation.

Graphene nanodots-encaged porous gold electrode fabricated via ion beam sputtering deposition for electrochemical analysis of heavy metal ions

All rights reserved. A graphene nanodots-encaged porous gold electrode via ion beam sputtering deposition (IBSD) for electrochemical sensing is presented. The electrodes were fabricated using Au target, and a composite target of Al and graphene, which were simultaneously sputtered onto glass substrates by Ar ion beam, followed with hydrochloric acid corrosion. The as-prepared graphene nanodots-encaged porous gold electrodes were then used for the analysis of heavy metal ions, e.g. Cu2+ and Pb2+ by Osteryoung square wave voltammetry (OSWV). These porous electrodes exhibited enhanced detection range for the heavy metal ions due to the entrapped graphene nanodots in 3-D porous structure. In addition, it was also found that when the thickness of porous electrode reached 40 nm the detection sensitivity came into saturation. The linear detection range is 0.009-4 μM for Cu2+ and 0.006-2.5 μM for Pb2+. Good reusability and repeatability were also observed. The formation mechanism and 3-D structure of the porous electrode were also investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectra (XPS). This graphene entrapped 3-D porous structure may envision promising applications in sensing devices.

A highly conductive porous graphene electrode prepared via in situ reduction of graphene oxide using Cu nanoparticles for the fabrication of high performance supercapacitors

Herein, a new graphene/Cu nanoparticle composite was prepared via the in situ reduction of GO in the presence of Cu nanoparticles which was then utilized as a sacrificing template for the formation of flexible and porous graphene capacitor electrodes by the dissolution of the intercalated Cu nanoparticle in a mixed solution of FeCl3 and HCl. The porous RGO electrode was characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The as-prepared graphene/Cu nanoparticle composite and the pure graphene film after removal of Cu nanoparticles possessed high conductivity of 3.1 × 10³ S m^-1 and 436 S m^-1 respectively. The porous RGO can be used as the electrode for the fabrication of supercapacitors with high gravimetric specific capacitances up to 146 F g^-1, good rate capability and satisfactory electrochemical stability. This environmentally friendly and efficient approach to fabricating porous graphene nanostructures could have enormous potential applications in the field of energy storage and nanotechnology.

Superior adsorption of pharmaceutical molecules by highly porous BN nanosheets

Highly porous boron nitride nanosheets (BNNSs) were tested as a re-usable adsorbent for the removal of pharmaceuticals from aqueous solution. The BNNSs exhibit both unprecedentedly high adsorption capacities and excellent recyclability while maintaining their high adsorption capacity by a simple regeneration process. These advantages render BNNSs a promising material for water remediation applications.